Bulking and foaming of activated sludge in waste water treatment due to proliferation of Microthrix parvicella and other microorganisms is one of the greatest operational problems facing biological, and especially nutrient removal, waste water treatment plants. Because of the microorganisms' cell surface hydrophobicity (CSH), these microorganisms have been known to float in the surfaces of the treatment tanks.
The biggest problem is the production of a brown, viscous foam. Due to the tenacious nature of the foam, serious problems can develop as foam accumulates. The foaming can create safety hazards, deteriorate effluent quality, and be a source of odors. Furthermore since this type of foaming is associated with cold winter temperatures, the stabilized foam layer may freeze and may cause operational problems. Excessive bulking, or the weakness of the solids to settle, can also occur in the settling tanks, due to the presence of Microthrix parvicella and other filamentous microorganisms.
Though the causes of this type of foam causing microorganisms' growth are not very well defined, it is commonly associated with colder climates, long solids retention time (SRT), and the presence of lipids and fatty acids that are used for the microorganism's carbon source.
Existing foaming control methods may be successful in alleviating some of the symptoms, but generally, there are no quick solution and high foaming level can linger for months. Furthermore some suggested methods for foam control can result in inadequate treatment, and deteriorate effluent quality. Chemical anti-foaming agents used to suppress foaming are usually not effective in the long term. Disinfectant (typically chlorine solution) applied to the return activated sludge (RAS) for bulking control, is not always successful in controlling these microorganisms.
Microthrix parvicella or other microorganisms foaming is most prevalent in activated sludge type of treatment plants especially nutrient removal plants. Conventional activated sludge treatment plants consists of bar screening, aerated grit removal, primary sedimentation, and activated sludge biological treatment. The sludge collected in these processes is then typically anaerobically digested and dewatered. FIG. 1 is a schematic of typical activated sludge treatment plant for which this invention is most applicable to.
Once foam causing microorganisms has been established in a conventional activated sludge plant control options have had limited success. Because of the hydrophobic nature of these microorganisms they float at the top of aeration basins and thus they are often trapped in the basins since outlets are submerged.